Coastal environments shape chemical and microbial properties of forest litters in the Circum‐Mediterranean region

This study explores how chemical and microbial properties of litters can be affected by coastal environments across the Mediterranean basin. A litterbag experiment including Pinus halepensis Mill. and Pistacia lentiscus L., collected from both inland and coastal areas, was set up in France, Greece and Algeria. Control litterbags were left in their sampling sites and a transfer of litterbags from inland to coastal areas was performed to test whether the effect of the specific constraints of coastal environments varies according to the country and the litter type. After 10 months, litter chemical composition (CP/MAS 13C‐NMR) and microbial activities (cellulase activity, basal respiration, catabolic diversity using Biolog) and community structure (TRFLP) were analysed. Coastal conditions led to various responses: (i) litter aromaticity differed in the coastal zones depending on the country (high in the Greek coastal area, low in the Algerian coastal zone), (ii) fewer functionally diversified microbial communities were found in the Greek coastal area compared to the French and Algerian coasts, (iii) genetic diversity and richness were strongly impacted after transfer to the coastal zone whatever the country. The type of litter shaped microbial communities: (i) at a local scale (i.e., in either coastal or inland areas) catabolic profiles and cellulase activities varied with the plant species, (ii) at a regional scale, the effect of coastal conditions differed with the plant species (basal respiration, Shannon‐Weaver index, catabolic diversity H′, cellulases and catabolic profiles). Thus, litter microbial properties differed in coastal environments across the Mediterranean basin and plant litter type plays a major role in microbial properties at a large spatial scale. Highlights The environmental drivers of litter microbial sensitivity to water potential stress were investigated Litterbag transfers from inland to coastal areas were performed in the Mediterranean. Soil and land system units conform to long‐tail or heavy tail distributions. Microbial diversity of inland litters decreased when exposed to coastal conditions Litter plant species shape microbial functioning even at wide spatial scales. Coastal areas and plant litter drive microbial responses to water potential stress.